1. Field of the Invention
The present invention relates to plastic containers which are suitable for receiving a hot fill product.
The term "container" is understood herein to mean any type of container, including, but not limited to, bottles and jars.
The present invention relates particularly, although by no means exclusively, to hot fill bottles formed from blow-moulded polyester resin.
2. Present State of the Art
Hot fill bottles are well known in the liquid packaging industry. In general terms, hot fill bottles are bottles that are filled with a liquid product that is hot, typically at least 80.degree. C., and thereafter are sealed while the liquid is hot in order to provide adequate sterilisation.
Commonly, hot fill bottles are blow moulded from polyester resin and other suitable polymeric materials and comprise a base, a generally cylindrical body, a shoulder, and a neck.
Hot fill bottles manufactured from blow moulded polyester resin do not expand significantly on contact with hot liquid. However, as hot liquid cools, usually it contracts and thereby creates a partial vacuum in the sealed bottles. The partial vacuum generates inward forces on the walls of the bottles. Unless the inward forces are resisted by the structure of the bottles or the shape of the bottles change in a controlled manner in response to the inward forces, there is uncontrolled distortion of the walls of the bottles.
In many situations, uncontrolled distortion of hot fill bottles results in the bottles having a mis-shapen/buckled appearance which consumers assume is an indication that the bottles are damaged, and thereby detracts from the marketability of the bottles.
In order to avoid uncontrolled distortion of the walls of hot fill bottles, a known type of hot fill bottle comprises an even number of circumferentially spaced concave panels arranged in diametrically opposed pairs in the cylindrical body of the bottle. The concave panels do not resist the internal pressure changes as hot liquid cools in the bottle but respond to the changes by flexing or deforming inwardly as hot liquid in the sealed bottles contracts as it cools in the bottles.
Whilst this known type of hot fill bottle is able to accommodate typical volume reductions in current hot-fill applications, the concave panels form a significant part of the body of the bottle and provide inadequate support for a label to be wrapped around the bottle. In marketing terms, this is a significant disadvantage of the bottle.
As a consequence, a known modified hot fill bottle comprises concave panels having central raised label support sections which define contact areas for labels.
The use of the label support sections addresses the need to provide sufficient contact area for labels. However, a disadvantage is that the label support sections are relatively rigid and reduce the volume that can be accommodated by the panels--with the effect on volume reduction being directly related to the relative surface areas of the label support sections and the concave sections of the panels.
It has been found that the maximum volume reduction that can be accommodated by commercially available hot fill bottles having label support sections is close to the typical volume reduction of liquids that occurs in current hot-fill applications when the liquids cool from hot fill temperatures (at least 80.degree. C.) to ambient temperature. As a consequence, in practice, it has been found that the panels of a significant percentage of the commercially available hot fill bottles are not able to move inwardly sufficiently to accommodate the reductions in volume and, consequently, these bottles collapse and distort in an uncontrolled manner.
One possible solution to this problem is to increase the wall thickness of the hot fill bottles. However, this solution carries with it a relatively high economic cost due to additional raw materials and handling costs.